Heater blows cold air

Could be gas has leaked out causing low pressure and no cold air!

The heater core is possibly blocked or the temperature adjuster is not working.

First check the controls to be certain that the temperature aduster is working and the flaps/doors that direct the flow of hot air are working.

If they are..........

Check heater hose temp. If one is hot and one is cold, you are not getting flow through the heater core.

Bleed it to remove an air blockage.
If that does not work, flush the system.
If that does not work, replace the heater core.

Karl at topgunwon.com

if all else fails, change thermostat, and bleed are from system if needbe.

replace your thermostat and flush your system

CHECK COOLANT MAKE SURE ITS NOT LOW.IF COOLANT GOOD THERMOSTAT BAD.

THE HEATER CONTROL VALVE MAY BE BAD OR A VACCUM HOSE OFF OR LEAKING SOMEWHERE

First you have to identify what causes the problem.
To do this you have to:
1) When engine is cold check the level of coolant. If it is low fill it up.
2) Start engine and check if engine reaches regular temperature. If your engine is not heated enough it means your thermostat does not work properly and should be replaced.
3) If engine temperature is normal, then check the temperature of pipes that go to/from heater core. These pipes are located up the fire wall (easier access is from the passenger side). If pipe/pipes are cold (even engine is worm) it means you heater core is plugged and should be flushed. Keep in mind, flushing the whole cooling system is different from flushing heater core.
4) If pipe/pipes are hot/warm, turn off the fan, switch controller to the hot position, wait for 3-4 minutes and turn on the fan. Note if the cold air blows first or warm air blows first but it cools down in 5-10 seconds. If the air blows cold than it is most probably the problem with blend door or blend door actuator.
5) If air blows warm first and then cools down, then while running engine and remaining the transmission in PARKING position, press on the gas pedal until your engine reaches 3,000 RPM. Check if your heater blows warm/hot air. If it does, then your water pump does not work properly and should be replaced. If the air still cold, I would suggest to flush the heater core.

First you have to identify what causes the problem.
To do this you have to:
1) When engine is cold check the level of coolant. If it is low fill it up.
2) Start engine and check if engine reaches regular temperature. If your engine is not heated enough it means your thermostat does not work properly and should be replaced.
3) If engine temperature is normal, then check the temperature of pipes that go to/from heater core. These pipes are located up the fire wall (easier access is from the passenger side). If pipe/pipes are cold (even engine is warm) it means you heater core is plugged and should be flushed. Keep in mind, flushing the whole cooling system is different from flushing heater core.
4) If pipe/pipes are hot/warm, turn off the fan, switch controller to the hot position, wait for 3-4 minutes and turn on the fan. Note if the cold air blows first or warm air blows first but it cools down in 5-10 seconds. If the air blows cold than it is most probably the problem with blend door or blend door actuator.
5) If air blows warm first and then cools down, then while running engine and remaining the transmission in PARKING position, press on the gas pedal until your engine reaches 3,000 RPM. Check if your heater blows warm/hot air. If it does, then your water pump does not work properly and should be replaced. If the air still cold, I would suggest flushing the heater core.

try to back flush the heater core. and if that dont work check the blend door it see if it is working.

Have the cooling system flushed or remove the hoses from the firewall(when cool) and blow out heater core with compressed air-clogged heater core..